YOur on the right track with your questions, I would also ask them how many deals they do in a typical year, if they will be using cash or a creditline, or financing. If they are serious buyers ask them if they can provide a verification of cash funds or a prepproval letter prior to assigning them a contract or wrtiing up a contract with you. Once you have done a deal or two with them then you can let down your guard.
It is extremely important to build a quality buyers list before tyeing up properties, Many of the people that you end up talking to will be all talk and no action, and the last thing you want to do is find out your buyers list is all fluff and no stuff, when it comes time to close on a home.